Hydrogen and Oxygen Stable Isotope Ratios of Milk in the United States

Models of hydrogen and oxygen incorporation in human tissues recognize the impact of geographic location on the isotopic composition of fluid intake, but inputs can include nonlocal beverages, such as milk. Milk and cow drinking water were collected from dairies, and commercially available milk was purchased from supermarkets and fast food restaurants. It was hypothesized that milk water δ2H and δ18O values record geographic location information. Correlations between milk water isotope ratios and purchase location tap water were significant. However, the amount of variation in milk δ2H and δ18O values explained by tap water was low, suggesting a single estimation of fluid input isotope ratios may not always be adequate in studies. The δ2H and δ18O values of paired milk and cow drinking water were related, suggesting potential for geographical origin assignment using stable isotope analysis. As an application example, milk water δ18O values were used to predict possible regions of origin for restaurant samples.